It is your opposite, but also your complementary Sign.
It can strongly attract you or systematically push you away!
This is true for Birth Signs, Ascendants or a dominance of planets in one Sign.
For example, you could have a planetary cluster in Aries at your birth and be drawn towards someone with a Libra Rising Sign, even though Aries is not your Sun Sign.
Now, you may better understand why you may fancy an individual or dislike them intensely!